igneous
Iron-stained porphyritic volcanic rock (possibly altered tuff)
Likely porphyritic andesite or volcanic tuff; exact identification requires examination of a fresh surface
AI-generated identification · may be incorrectOchre-brown, fine-grained matrix with scattered pale, rounded to angular grains or crystals; iron-oxide staining gives an earthy, dull luster. Hardness and crystal structure cannot be reliably determined from the photograph.
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Physical properties
Ochre-brown, fine-grained matrix with scattered pale, rounded to angular grains or crystals; iron-oxide staining gives an earthy, dull luster. Hardness and crystal structure cannot be reliably determined from the photograph.
Formation & geological history
Probably formed from volcanic ash or lava containing larger crystals, then altered and stained by iron-bearing fluids; its age and precise setting cannot be determined visually.
Uses & applications
Small specimens are mainly of geological or hobby interest; volcanic rocks may be used as aggregate or decorative stone when available in larger quantities.
Geological facts
The pale spots may be mineral grains, altered crystals, or small inclusions rather than fossils. The rusty color commonly results from iron oxides such as limonite or goethite.
Field identification & locations
Look for a fine volcanic groundmass with embedded pale grains and iron staining; compare a fresh break and test hardness before naming it more precisely. Similar altered volcanic rocks occur in volcanic regions worldwide.
